We’ve all got that one friend – the one who arrives at a party looking like Kate Moss ready for a Testino shoot, shrugging nonchalantly: ‘This old thing? 50p in a charity shop.’

A desire to be that girl has led me charity shopping many a time – but I’ve always gone home empty-handed and exhausted.

But British charity shops are booming. They’ve shot up in number by 30 per cent since 2008 and, despite an overall dip in profits last year, have generally performed well as other high-street retailers struggled to survive the recession.

Besides hunting for elusive fashion treasure, there are sound reasons to scour charity shop rails. Brits send a mammoth 350,000 tonnes of used clothing to landfill each year, according to recycling experts Wrap.

The rise of secondhand stores has helped to cut what we bin. In fact, it has been estimated they reduce Britain’s CO2 emissions by a million tonnes a year – almost the entire carbon footprint of Iceland.

And there’s more. The rise of cheap, fast fashion usually means someone is losing out along the way, and that someone is generally a poorly paid garment worker in unsafe conditions. Then there’s the environmental cost of manufacturing to be considered. So buying used rather than new is often the green thing to do – although that doesn’t mean it’s easy.

At the Traid store in Dalston, east London, I seek some much-needed advice on pulling together an on-trend look in a charity shop. Hannah Lane of Redress, a Hong Kong-based non-governmental organisation that promotes sustainability in fashion, and stylist Fabienne Hebrard are on hand to help.

Amy scours the racks for bargains (Picture: Daniel Lynch)

Redress’s CEO, Christina Dean, is attempting to wear only dumped or donated clothing for an entire year. I’ve been following her challenge on Instagram for a while. Unfortunately for me, where Dean is tall, willowy and blonde, I am just… tall. So I’m keen to find out if charity shopping, with its jumble of sizes and styles, can actually make someone less model-esque look good.

The store is laid out like a cool boutique but retains that distinctive charity-shop colour-coding that makes everything easier to rifle through. And, although I’ve known some second-hand stores to smell a bit like mushrooms left at the back of the fridge, there’s not a whiff of that here. Within minutes, we’ve spotted a pink vintage Yves Saint Laurent skirt suit, which thrills Hebrard.

She gives me some good advice on stress-free charity shopping: ‘Always go in knowing what you want to look for, because it gets very overwhelming otherwise. But fashion is cyclical and most trends come around again and again – so charity shops are the perfect mining ground.’

Why go for faux retro denim from New Look, when you can nab the real thing and look a lot cooler?

Hebrard suggests we look for leather and monochrome – as well as nods to the current grunge revival. I already accidentally dress like a 1990s teenager most of the time, so this sounds great to me.

She finds me a Vivienne Westwood-style tartan kilt but it’s a bit small – and the danger with charity shopping is, of course, that if you fall in love with something that doesn’t fit there are no other sizes. The flip side is that it feels much more special when you find something perfect – and I’m chuffed when we find a leather skirt that fits like a glove.

Across the country, perhaps at least partly inspired by the Mary Queen Of Charity Shops TV series, more and more stores are making themselves over – just check out one of the stylish Oxfam Boutiques. Last year, the Beckhams even donated a huge haul to the Red Cross shop in Chelsea, to help the Filipino victims of Typhoon Haiyan. In fact it’s been argued that the high prices found in some charity shops are rendering them the preserve of rich label-hunters.

It is true that not all of us can afford designer cast-offs such as the YSL suit that so thrilled Hebrard and carried a price tag of £100. But my leather skirt was a steal at £18.99.

In fact most of the charity stores I visit, especially outside of central London, are still selling incredibly affordable clothes which come without the guilt associated with buying comparably priced new clobber. And I’m surprised to discover that many organisations, such as Oxfam, even sell donated clothes online – truly making life easy.

So I’m a charity shop convert. But ultimately, I know I’m never going to eliminate new clothes from my wardrobe as Dean has – the allure of the ‘New In’ tab on Asos or Topshop is sometimes just going to be too much. But, with a bit of focus, charity shopping can be a fun and sustainable first port of call on your fashion quest.

Following Christina Dean’s 365 Challenge in 2013, the Get Redressed Challenge 2014 invites everyone to join in. Follow the results on Instagram @GetRedressed and get involved. www.redress.com.hk

How to find charity shop gemsGo in with a clear idea of what you’re hunting for, otherwise things can get overwhelming. But have fun! Don’t be afraid to try things you normally wouldn’t, too.

Look for certain core trends and fabrics that come into fashion again and again. As stylist Fabienne Hebrard says: ‘If your wardrobe’s got a bit of leather, a bit of monochrome and a bit of animal print, you can’t go wrong.’

Choose your area – charity shops tend to reflect their surroundings. Try upmarket, boutique-y areas for designer clobber or streets full of indie record stores and art galleries for on-trend cast-offs.

With a little bit of effort, you can transform items into your dream garms. Hems can be raised, tops can be lengthened with a trim, zips can be fixed.